1. Field of the Invention
The present invention is generally related to a transmission actuation system and, more particularly, to a hydraulically assisted shift mechanism that is configured to move a marine transmission between forward, neutral and reverse gear positions.
2. Description of the Related Art
Those skilled in the art of marine propulsion systems are aware of many different types of shifting mechanisms that can be used to move a transmission between forward, neutral and reverse gear positions. Typical marine transmissions, particularly for use in conjunction with outboard motors and sterndrive systems, use mechanical linkages to perform these functions. Some transmissions are hydraulically assisted and use pressurized hydraulic fluid to move an actuator between various gear positions. Typically, a hydraulic pump is driven by a driveshaft of the outboard motor to generate pressurized hydraulic fluid that is ported to appropriate cavities and conduits to move an actuator.
U.S. Pat. No. 3,623,583, which issued to Shimanckas on Nov. 30, 1971, describes an electrically operated control mechanism for a hydraulic shifting mechanism. It includes a hydraulic mechanism which is operative to effect shifting of a clutch from a fail-safe forward drive condition to either of a neutral or reverse condition. Also disclosed is an electrically operated control mechanism for the hydraulic mechanism, which control mechanism is also designed to fail safe in forward drive. The mechanism includes aligned, neutral and rearward drive solenoids which are selectively energizeable to afford neutral and reverse drive and which are operably associated with a single plunger carrying a spool valve embodied in the hydraulic system.
U.S. Pat. No. 3,919,964, which issued to Hagen on Nov. 18, 1975, describes a marine propulsion reversing transmission with hydraulic assist. It is located in a propulsion unit and connects a driveshaft to a propeller shaft. It is shiftable between neutral, forward drive, and rearward drive conditions. A mechanical linkage includes a shift actuator carried by the propeller shaft for common rotary movement with the propeller shaft and for axial movement relative to the propeller shaft and connected to a clutch dog for common movement therewith, together with a rod movable transversely of the shift actuator and a coupling connecting the rod and the shift actuator for effecting shift actuator movement in one direction axially of the propeller shaft in response to rod movement in one direction transversely of the propeller shaft and for effecting shift actuator movement in the other direction in response to rod movement in the other direction and for simultaneously permitting rotary shift actuator movement relative to the rod.
U.S. Pat. No. 3,922,997, which issued to Jameson on Dec. 2, 1975, describes a marine power transmission system. It has an input shaft for connection to a single main propulsion engine, a pair of parallel output shafts and a pair of fluid actuated friction clutches disposed on each output shaft for selectively engaging gear sets to drive the output shafts in the same or opposite directions of rotation independently or simultaneously.
U.S. Pat. No. 5,328,396, which issued to Hayasaka on Jul. 12, 1994, describes a power transmission system for an inboard/outboard motor. A hydraulic pump for actuating clutches and for lubricating the transmission is driven off the rear end of the input shaft and control valve means selectively communicating the fluid from the hydraulic pump with the hydraulic clutches. The valve means is a rotary plug type valve but is constructed so as to minimize axial and radial forces acting that would tend to bind its movement.
U.S. Pat. No. 5,902,160, which issued to Weronke et al. on May 11, 1999, discloses a twin propeller marine propulsion unit. A vertical driveshaft is journaled in a lower gear case and drives a pair of bevel gears. A pair of concentric propeller shafts are mounted in the lower torpedo section of the gear case and each shaft carries a propeller. A slidable clutch is movable between a neutral, a forward, and a reverse position and serves to operably connect the outer propeller shaft with one of the bevel gears when the clutch is moved to the forward drive position.
U.S. Pat. No. 6,062,926, which issued to Alexander et al. on May 16, 2000, discloses a hydraulic system for a dual propeller marine propulsion unit. An improved hydraulic system for a twin propeller marine propulsion unit is described in which a vertical driveshaft is operably connected to the engine of the propulsion unit and carries a pinion that drives a pair of coaxial bevel gears. An inner propeller shaft and an outer propeller shaft are mounted concentrically in the lower torpedo section of the gear case and each propeller shaft carries a propeller. The hydraulic system includes a pump connected to the inner propeller shaft, and the pump has an inlet communicating with a fluid reservoir in the gear case and has an outlet which is connected through a hydraulic line to the multi-disc clutch.
U.S. Pat. No. 6,129,599, which issued to Hallenstvedt et al. on Oct. 10, 2000, describes a transmission assembly for a marine vessel. An electrically controlled transmission system for a marine vessel is adapted to avoid vibration to the vessel during a shifting process of the transmission system.
U.S. Pat. No. 6,176,750, which issued to Alexander et al. on Jan. 23, 2001, discloses a marine propulsion unit with a hydraulic pump. A hydraulically operated multi-disc clutch is actuated when engine speed reaches a pre-selected elevated value to operably connect the second of the bevel gears to an outer propeller shaft, to thereby drive the second propeller in an opposite direction to a first propeller.
U.S. Pat. No. 6,884,131, which issued to Katayama et al. on Apr. 26, 2005, describes a shift mechanism for a marine propulsion unit. An outboard motor incorporates a driveshaft and a propulsion shaft driven by the driveshaft. The driveshaft carries a pinion. The propulsion shaft carries forward and reverse gears. The pinion always meshes with the forward and reverse gears and drives the forward and reverse gears in opposite directions relative to each other. A hydraulic forward clutch mechanism couples the forward gear with the propulsion shaft. A hydraulic reverse clutch mechanism couples the reverse gear with the propulsion shaft.
U.S. Pat. No. 7,104,857, which issued to Swan et al. on Sep. 12, 2006, discloses a method for controlling a hydraulically assisted steering system of a marine vessel. The system provides a controller which activates a hydraulic pump when a manual throttle selector handle is in either forward or reverse gear selector positions, but deactivates the pump when the handle is in a neutral gear selector position. A controller can also interrogate an ignition key to make sure that it is in an on position and also respond to the activation of a manual switch which can be used to override the deactivation step of the pump.
U.S. patent application Ser. No. 11/786,821, which was filed on Apr. 13, 2007 (M10112) by Phillips et al., discloses an actuator device for a marine propulsion transmission. The actuator is attached to a movable clutch member through the use of a coupler which comprises a generally spherical member formed as a portion of the actuator and a chuck device formed as part of the clutch member. The generally spherical member, or alternatively shaped component, is received by the chuck device and retained therein. The components are configured to allow relative rotation between the actuator and the clutch member while causing them to move axially in synchrony with each other.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
In some marine transmissions, greater force is needed to move a transmission into a neutral position, from either a forward or reverse position, than is normally required to move the transmission into a forward or reverse gear position from the neutral position. On the other hand, it is often desirable to move the transmission into either forward or reverse gear, from a neutral position, more swiftly than when the transmission is moved into neutral from either a forward or reverse gear position. It would therefore be significantly beneficial if an actuator system could be provided that provides greater force to move the transmission out of gear, into a neutral position, than is provided to move the transmission into gear. It would also be beneficial if the speed of actuation into gear, from a neutral position, could be provided which is greater than the speed in which the actuator moves the transmission out of gear. Furthermore, it would be significantly beneficial if an actuator could be provided which is simple in structure and operation and relatively inexpensive to manufacture and assemble.